1. Field
Aspects of embodiments of the present invention relate to an adhesive film for polarizing plates, polarizing plate including the same, and an optical display including the same.
2. Description of the Related Art
A liquid crystal display includes a liquid crystal panel and polarizing plates attached to both surfaces of the liquid crystal panel. Each of the polarizing plates includes a polarizer and a protective film formed on one or both surfaces of the polarizer to protect the polarizer. The polarizing plate is attached to the liquid crystal panel via an adhesive film for polarizing plates. The adhesive film for polarizing plates is formed of an adhesive composition for polarizing plates.
A polarizing plate on a glass plate such as a liquid crystal panel has high pencil hardness. However, when measured after attaching the polarizing plate to such a glass plate via an adhesive film for polarizing plates, the pencil hardness of the polarizing plate on the adhesive film is lower than that of the polarizing plate on the glass plate. When the polarizing plate attached to the liquid crystal panel via the adhesive film exhibits low pencil hardness, the polarizing plate is not suitable for use in optical displays.
An adhesive film for polarizing plates having high modulus can increase pencil hardness of a polarizing plate on the adhesive film. However, an adhesive film exhibiting high modulus at high temperature can cause light leakage and deterioration in durability, such as detachment of the polarizing plate, dragging, or generation of bubbles. Light leakage, durability deterioration, and the like occur due to shrinkage of the polarizers by heat and/or moisture. Therefore there is a need for an adhesive film for polarizing plates, which can act as a hard type adhesive film having high modulus at room temperature so as to increase pencil hardness of a polarizing plate on the adhesive film and can act as a soft type adhesive film having low modulus at high temperature so as to suppress light leakage while improving durability. A typical hard type adhesive film has low modulus at high temperature. However, the degree of modulus reduction at high temperature is significantly low, thereby causing light leakage or poor durability at high temperature.
The background technique of the present invention is disclosed in Japanese Patent Publication No. 2015-010192 A.